@Test
    public void TestPair() {
        Pair<String,String> pair = Pair.of("left","right");
        System.out.println("left = " + pair.getLeft());
        System.out.println("right = " + pair.getRight());
        System.out.println("key = " + pair.getKey());
        System.out.println("value = " + pair.getValue());
        Pair<String,String> mutablePair = new MutablePair<>("left","right");
        System.out.println("-----------------------mutablePair------------------------");
        System.out.println("left = " + pair.getLeft());
        System.out.println("right = " + pair.getRight());
        System.out.println("key = " + pair.getKey());
        System.out.println("value = " + pair.getValue());
        Pair<String,String> immutablePair = new ImmutablePair<>("left","right");
        System.out.println("-----------------------immutablePair------------------------");
        System.out.println("left = " + pair.getLeft());
        System.out.println("right = " + pair.getRight());
        System.out.println("key = " + pair.getKey());
        System.out.println("value = " + pair.getValue());
    }

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package org.apache.commons.lang3.tuple;

import java.io.Serializable;
import java.util.Objects;
import java.util.Map.Entry;
import org.apache.commons.lang3.builder.CompareToBuilder;

public abstract class Pair<L, R> implements Entry<L, R>, Comparable<Pair<L, R>>, Serializable {
    private static final long serialVersionUID = 4954918890077093841L;

    public Pair() {
    }
    // 默認(rèn)用的是子類ImmutablePair，
    public static <L, R> Pair<L, R> of(L left, R right) {
        return new ImmutablePair(left, right);
    }
    // 定義了抽象方法，目的子類去實(shí)現(xiàn)
    public abstract L getLeft();
    // 定義了抽象方法，目的子類去實(shí)現(xiàn)
    public abstract R getRight();
    // 這里的獲取key其實(shí)就是獲取getLeft()方法的值
    public final L getKey() {
        return this.getLeft();
    }
    // 這里的獲取value  其實(shí)就是獲取getRight()方法的值
    public R getValue() {
        return this.getRight();
    }
    // 這里就是比較兩個(gè)Pair
    public int compareTo(Pair<L, R> other) {
        return (new CompareToBuilder()).append(this.getLeft(), other.getLeft()).append(this.getRight(), other.getRight()).toComparison();
    }

    public boolean equals(Object obj) {
        if (obj == this) {
            return true;
        } else if (!(obj instanceof Entry)) {
            return false;
        } else {
            Entry<?, ?> other = (Entry)obj;
            return Objects.equals(this.getKey(), other.getKey()) && Objects.equals(this.getValue(), other.getValue());
        }
    }

    public int hashCode() {
        return (this.getKey() == null ? 0 : this.getKey().hashCode()) ^ (this.getValue() == null ? 0 : this.getValue().hashCode());
    }

    public String toString() {
        return "(" + this.getLeft() + ',' + this.getRight() + ')';
    }

    public String toString(String format) {
        return String.format(format, this.getLeft(), this.getRight());
    }
}

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package org.apache.commons.lang3.tuple;
// 繼承了Pair
public final class ImmutablePair<L, R> extends Pair<L, R> {
    private static final ImmutablePair NULL = of((Object)null, (Object)null);
    private static final long serialVersionUID = 4954918890077093841L;
    // 這里用了final修飾，代表的left值設(shè)值之后是不可變
    public final L left;
    // 這里用了final修飾，代表的right值設(shè)值之后是不可變
    public final R right;

    public static <L, R> ImmutablePair<L, R> nullPair() {
        return NULL;
    }

    public static <L, R> ImmutablePair<L, R> of(L left, R right) {
        return new ImmutablePair(left, right);
    }

    public ImmutablePair(L left, R right) {
        this.left = left;
        this.right = right;
    }

    public L getLeft() {
        return this.left;
    }

    public R getRight() {
        return this.right;
    }
    // 因?yàn)槭遣豢勺兊闹?，所以如果set值的話直接拋異常
    public R setValue(R value) {
        throw new UnsupportedOperationException();
    }
}

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package org.apache.commons.lang3.tuple;

public class MutablePair<L, R> extends Pair<L, R> {
    private static final long serialVersionUID = 4954918890077093841L;
    public L left;
    public R right;

    public static <L, R> MutablePair<L, R> of(L left, R right) {
        return new MutablePair(left, right);
    }

    public MutablePair() {
    }

    public MutablePair(L left, R right) {
        this.left = left;
        this.right = right;
    }

    public L getLeft() {
        return this.left;
    }

    public void setLeft(L left) {
        this.left = left;
    }

    public R getRight() {
        return this.right;
    }

    public void setRight(R right) {
        this.right = right;
    }
    // 這里set value值，會(huì)返回舊value值
    public R setValue(R value) {
        R result = this.getRight();
        this.setRight(value);
        return result;
    }
}