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dunwudunwu
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update codes and docs
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11 files changed

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‎assets/JVM/Java故障排查.eddx

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‎assets/JVM/Java故障排查.xmind

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‎codes/javacore-basics/src/main/java/io/github/dunwu/javacore/datatype/BigDecimal判等.java

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package io.github.dunwu.javacore.datatype;
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import java.math.BigDecimal;
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import java.util.HashSet;
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import java.util.Set;
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import java.util.TreeSet;
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/**
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* @author <a href="mailto:forbreak@163.com">Zhang Peng</a>
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* @since 2020-08-11
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*/
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public class BigDecimal判等 {
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public static void main(String[] args) {
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System.out.println("====================== wrong ======================");
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wrong();
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System.out.println("====================== right ======================");
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right();
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System.out.println("====================== set ======================");
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set();
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}
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private static void wrong() {
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System.out.println(new BigDecimal("1.0").equals(new BigDecimal("1")));
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}
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private static void right() {
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System.out.println(new BigDecimal("1.0").compareTo(new BigDecimal("1")) == 0);
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}
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private static void set() {
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Set<BigDecimal> hashSet1 = new HashSet<>();
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hashSet1.add(new BigDecimal("1.0"));
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System.out.println(hashSet1.contains(new BigDecimal("1")));//返回false
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Set<BigDecimal> hashSet2 = new HashSet<>();
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hashSet2.add(new BigDecimal("1.0").stripTrailingZeros());
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System.out.println(hashSet2.contains(new BigDecimal("1.000").stripTrailingZeros()));//返回true
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Set<BigDecimal> treeSet = new TreeSet<>();
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treeSet.add(new BigDecimal("1.0"));
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System.out.println(treeSet.contains(new BigDecimal("1")));//返回true
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}
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}

‎codes/javacore-basics/src/main/java/io/github/dunwu/javacore/datatype/数值溢出.java

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package io.github.dunwu.javacore.datatype;
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import java.math.BigInteger;
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/**
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* @author <a href="mailto:forbreak@163.com">Zhang Peng</a>
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* @since 2020-08-11
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*/
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public class 数值溢出 {
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public static void main(String[] args) {
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System.out.println("====================== wrong1 ======================");
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wrong();
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System.out.println("====================== right1 ======================");
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right1();
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System.out.println("====================== right2 ======================");
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right2();
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}
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private static void wrong() {
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long l = Long.MAX_VALUE;
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System.out.println(l + 1); // -9223372036854775808
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System.out.println(l + 1 == Long.MIN_VALUE); // true
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}
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private static void right1() {
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try {
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long l = Long.MAX_VALUE;
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System.out.println(Math.addExact(l, 1));
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} catch (Exception ex) {
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ex.printStackTrace();
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}
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}
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private static void right2() {
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BigInteger i = new BigInteger(String.valueOf(Long.MAX_VALUE));
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System.out.println(i.add(BigInteger.ONE).toString());
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try {
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long l = i.add(BigInteger.ONE).longValueExact();
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} catch (Exception ex) {
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ex.printStackTrace();
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}
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}
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}

‎codes/javacore-basics/src/main/java/io/github/dunwu/javacore/datatype/数值计算示例.java

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package io.github.dunwu.javacore.datatype;
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import lombok.extern.slf4j.Slf4j;
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import java.math.BigDecimal;
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/**
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* 使用 BigDecimal 表示和计算浮点数，且务必使用字符串的构造方法来初始化 BigDecimal
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*
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* @author <a href="mailto:forbreak@163.com">Zhang Peng</a>
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* @since 2020-08-11
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*/
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@Slf4j
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public class 数值计算示例 {
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public static void main(String[] args) {
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System.out.println("====================== wrong1 ======================");
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wrong1();
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System.out.println("====================== wrong2 ======================");
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wrong2();
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System.out.println("====================== right ======================");
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right();
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System.out.println("====================== testScale ======================");
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testScale();
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}
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/**
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* 浮点数计算结果不符合预期的场景
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*/
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private static void wrong1() {
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System.out.println(0.1 + 0.2); // 0.30000000000000004
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System.out.println(1.0 - 0.8); // 0.19999999999999996
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System.out.println(4.015 * 100); // 401.49999999999994
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System.out.println(123.3 / 100); // 1.2329999999999999
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double amount1 = 2.15;
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double amount2 = 1.10;
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System.out.println(amount1 - amount2); // 1.0499999999999998
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}
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/**
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* BigDecimal 不正确的初始化方式
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*/
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private static void wrong2() {
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System.out.println(new BigDecimal(0.1).add(new BigDecimal(0.2)));
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// Output: 0.3000000000000000166533453693773481063544750213623046875
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System.out.println(new BigDecimal(1.0).subtract(new BigDecimal(0.8)));
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// Output: 0.1999999999999999555910790149937383830547332763671875
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System.out.println(new BigDecimal(4.015).multiply(new BigDecimal(100)));
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// Output: 401.49999999999996802557689079549163579940795898437500
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System.out.println(new BigDecimal(123.3).divide(new BigDecimal(100)));
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// Output: 1.232999999999999971578290569595992565155029296875
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}
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/**
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* BigDecimal 正确的初始化方式
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*/
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private static void right() {
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System.out.println(new BigDecimal("0.1").add(new BigDecimal("0.2")));
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System.out.println(new BigDecimal("1.0").subtract(new BigDecimal("0.8")));
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System.out.println(new BigDecimal("4.015").multiply(new BigDecimal("100")));
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System.out.println(new BigDecimal("123.3").divide(new BigDecimal("100")));
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}
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/**
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* BigDecimal 浮点数精度测试
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*/
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private static void testScale() {
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BigDecimal bigDecimal1 = new BigDecimal("100");
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BigDecimal bigDecimal2 = new BigDecimal(String.valueOf(100d));
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BigDecimal bigDecimal3 = new BigDecimal(String.valueOf(100));
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BigDecimal bigDecimal4 = BigDecimal.valueOf(100d);
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BigDecimal bigDecimal5 = new BigDecimal(Double.toString(100));
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print(bigDecimal1); //scale 0 precision 3 result 401.500
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print(bigDecimal2); //scale 1 precision 4 result 401.5000
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print(bigDecimal3); //scale 0 precision 3 result 401.500
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print(bigDecimal4); //scale 1 precision 4 result 401.5000
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print(bigDecimal5); //scale 1 precision 4 result 401.5000
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}
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private static void print(BigDecimal bigDecimal) {
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log.info("scale {} precision {} result {}", bigDecimal.scale(), bigDecimal.precision(),
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bigDecimal.multiply(new BigDecimal("4.015")));
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}
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}

‎codes/javacore-basics/src/main/java/io/github/dunwu/javacore/datatype/浮点数舍入.java

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package io.github.dunwu.javacore.datatype;
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import java.math.BigDecimal;
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import java.math.RoundingMode;
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import java.text.DecimalFormat;
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/**
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* @author <a href="mailto:forbreak@163.com">Zhang Peng</a>
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* @since 2020-08-11
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*/
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public class 浮点数舍入 {
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public static void main(String[] args) {
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System.out.println("====================== wrong1 ======================");
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wrong1();
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System.out.println("====================== wrong2 ======================");
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wrong2();
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System.out.println("====================== right ======================");
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right();
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}
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private static void wrong1() {
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double num1 = 3.35;
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float num2 = 3.35f;
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System.out.println(String.format("%.1f", num1)); // 3.4
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System.out.println(String.format("%.1f", num2)); // 3.3
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}
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private static void wrong2() {
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double num1 = 3.35;
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float num2 = 3.35f;
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DecimalFormat format = new DecimalFormat("#.##");
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format.setRoundingMode(RoundingMode.DOWN);
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System.out.println(format.format(num1)); // 3.35
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format.setRoundingMode(RoundingMode.DOWN);
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System.out.println(format.format(num2)); // 3.34
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}
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private static void right() {
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BigDecimal num1 = new BigDecimal("3.35");
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BigDecimal num2 = num1.setScale(1, BigDecimal.ROUND_DOWN);
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System.out.println(num2); // 3.3
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BigDecimal num3 = num1.setScale(1, BigDecimal.ROUND_HALF_UP);
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System.out.println(num3); // 3.4
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}
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}

‎codes/javacore-container/src/main/java/io/github/dunwu/javacore/container/list/AsList示例.java

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package io.github.dunwu.javacore.container.list;
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import lombok.extern.slf4j.Slf4j;
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import java.util.ArrayList;
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import java.util.Arrays;
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import java.util.List;
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import java.util.stream.Collectors;
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/**
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* @author <a href="mailto:forbreak@163.com">Zhang Peng</a>
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* @since 2020-08-11
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*/
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@Slf4j
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public class AsList示例 {
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public static void main(String[] args) {
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System.out.println("====================== wrong1 ======================");
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wrong1();
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System.out.println("====================== right1 ======================");
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right1();
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System.out.println("====================== wrong2 ======================");
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wrong2();
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System.out.println("====================== right2 ======================");
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right2();
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}
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private static void wrong1() {
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int[] arr = { 1, 2, 3 };
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List list = Arrays.asList(arr);
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log.info("list:{} size:{} class:{}", list, list.size(), list.get(0).getClass());
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}
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private static void right1() {
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int[] arr1 = { 1, 2, 3 };
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List list1 = Arrays.stream(arr1).boxed().collect(Collectors.toList());
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log.info("list:{} size:{} class:{}", list1, list1.size(), list1.get(0).getClass());
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Integer[] arr2 = { 1, 2, 3 };
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List list2 = Arrays.asList(arr2);
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log.info("list:{} size:{} class:{}", list2, list2.size(), list2.get(0).getClass());
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}
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private static void wrong2() {
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String[] arr = { "1", "2", "3" };
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List list = Arrays.asList(arr);
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arr[1] = "4";
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try {
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list.add("5");
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} catch (Exception ex) {
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ex.printStackTrace();
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}
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log.info("arr:{} list:{}", Arrays.toString(arr), list);
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}
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private static void right2() {
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String[] arr = { "1", "2", "3" };
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List list = new ArrayList(Arrays.asList(arr));
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arr[1] = "4";
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try {
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list.add("5");
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} catch (Exception ex) {
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ex.printStackTrace();
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}
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log.info("arr:{} list:{}", Arrays.toString(arr), list);
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}
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}

‎codes/javacore-container/src/main/java/io/github/dunwu/javacore/container/list/SubList示例.java

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package io.github.dunwu.javacore.container.list;
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import java.util.ArrayList;
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import java.util.List;
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import java.util.stream.Collectors;
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import java.util.stream.IntStream;
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/**
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* @author <a href="mailto:forbreak@163.com">Zhang Peng</a>
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* @since 2020-08-11
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*/
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public class SubList示例 {
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public static void main(String[] args) throws InterruptedException {
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// oom();
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// oomfix();
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wrong();
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// right1();
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// right2();
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}
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private static List<List<Integer>> data = new ArrayList<>();
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private static void oom() {
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for (int i = 0; i < 1000; i++) {
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List<Integer> rawList = IntStream.rangeClosed(1, 100000).boxed().collect(Collectors.toList());
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data.add(rawList.subList(0, 1));
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}
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}
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private static void oomfix() {
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for (int i = 0; i < 1000; i++) {
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List<Integer> rawList = IntStream.rangeClosed(1, 100000).boxed().collect(Collectors.toList());
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data.add(new ArrayList<>(rawList.subList(0, 1)));
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}
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}
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private static void wrong() {
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List<Integer> list = IntStream.rangeClosed(1, 10).boxed().collect(Collectors.toList());
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List<Integer> subList = list.subList(1, 4);
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System.out.println(subList);
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subList.remove(1);
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System.out.println(list);
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list.add(0);
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try {
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subList.forEach(System.out::println);
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} catch (Exception ex) {
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ex.printStackTrace();
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}
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}
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private static void right1() {
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List<Integer> list = IntStream.rangeClosed(1, 10).boxed().collect(Collectors.toList());
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List<Integer> subList = new ArrayList<>(list.subList(1, 4));
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System.out.println(subList);
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subList.remove(1);
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System.out.println(list);
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list.add(0);
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subList.forEach(System.out::println);
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}
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private static void right2() {
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List<Integer> list = IntStream.rangeClosed(1, 10).boxed().collect(Collectors.toList());
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List<Integer> subList = list.stream().skip(1).limit(3).collect(Collectors.toList());
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System.out.println(subList);
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subList.remove(1);
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System.out.println(list);
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list.add(0);
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subList.forEach(System.out::println);
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}
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}

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