HashCode 和Equals 测试

class DiffHash_DiffEqual extends Base {

    public DiffHash_DiffEqual(String s) {
        this.s = s;
    }

    @Override
    public int hashCode() {
        int hash = 5;
        hash = 67 * hash + Objects.hashCode(this.s);
        return hash;
    }

    @Override
    public boolean equals(Object obj) {
        if (obj == null || getClass() != obj.getClass()) {
            return false;
        }
        final DiffHash_DiffEqual other = (DiffHash_DiffEqual) obj;
        return Objects.equals(this.s, other.s);
    }
}

class DiffHash_SameEqaul extends Base {

    public DiffHash_SameEqaul(String s) {
        this.s = s;
    }

    @Override
    public int hashCode() {
        int hash = 5;
        hash = 67 * hash + Objects.hashCode(this.s);
        return hash;
    }

    @Override
    public boolean equals(Object obj) {
        return true;
    }
}

class SameHash_DiffEqaul extends Base {

    public SameHash_DiffEqaul(String s) {
        this.s = s;
    }

    @Override
    public int hashCode() {

        return 1;
    }

    @Override
    public boolean equals(Object obj) {
        if (obj == null || getClass() != obj.getClass()) {
            return false;
        }
        final SameHash_DiffEqaul other = (SameHash_DiffEqaul) obj;
        return Objects.equals(this.s, other.s);
    }

}

class SameHash_SameEqual extends Base {

    public SameHash_SameEqual(String s) {
        this.s = s;
    }

    @Override
    public int hashCode() {

        return 1;
    }

    @Override
    public boolean equals(Object obj) {

        return true;
    }
}

class Base {

    protected String s;

    @Override
    public String toString() {
        return this.getClass().getSimpleName() + "{" + "s=" + s + '}';
    }

}

public class TestHashCodeEqals {

    public static void main(String[] args) {
        HashMap<DiffHash_DiffEqual, Integer> mapDiffHash_DiffEqual = new HashMap<>();
        mapDiffHash_DiffEqual.put(new DiffHash_DiffEqual("aaaaaa"), 1);
        mapDiffHash_DiffEqual.put(new DiffHash_DiffEqual("bbbbbb"), 2);
        System.out.println("DiffHash_DiffEqual ----------" + mapDiffHash_DiffEqual.keySet().size()  );
        
        HashMap<DiffHash_SameEqaul, Integer> mapDiffHash_SameEqaul = new HashMap<>();
        mapDiffHash_SameEqaul.put(new DiffHash_SameEqaul("aaaaaa"), 1);
        mapDiffHash_SameEqaul.put(new DiffHash_SameEqaul("bbbbbb"), 2);
        System.out.println("DiffHash_SameEqaul ----------" + mapDiffHash_SameEqaul.keySet().size()  );
        
        HashMap<SameHash_DiffEqaul, Integer> mapSameHash_DiffEqaul = new HashMap<>();
        mapSameHash_DiffEqaul.put(new SameHash_DiffEqaul("aaaaaa"), 1);
        mapSameHash_DiffEqaul.put(new SameHash_DiffEqaul("bbbbbb"), 2);
        System.out.println("SameHash_DiffEqaul ----------" + mapSameHash_DiffEqaul.keySet().size()  );
        
        HashMap<SameHash_SameEqual, Integer> mapSameHash_SameEqual = new HashMap<>();
        mapSameHash_SameEqual.put(new SameHash_SameEqual("aaaaaa"), 1);
        mapSameHash_SameEqual.put(new SameHash_SameEqual("bbbbbb"), 2);
        System.out.println("SameHash_SameEqual ----------" + mapSameHash_SameEqual.keySet().size()  );
    }
}

输出：
 DiffHash_DiffEqual ----------  2                         // 两个元素保存在不同内存地址
 DiffHash_SameEqaul----------   2                    // 两个元素保存在不同内存地址
 SameHash_DiffEqaul ----------2                      // 两个元素保存在相同内存地址，构成一个链表
 SameHash_SameEqual ---------- 1                //后一个元素替换了前一个元素