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  • 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


    
    
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  • 原文地址:https://www.cnblogs.com/leeeee/p/7276402.html
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