测试常量池

  1 public class TestConstantsPool {
  2     public static void main(String[] args) {
  3         integerPoolNewInteger();
  4     }
  5 
  6     static void stringPool() {
  7         String a = "a123";
  8         //用常量池
  9         String a_1 = a.intern();
 10         //用常量池
 11         String b = "a123";
 12         //不使用常量池
 13         String c = new String("a123");
 14 
 15         boolean e = a_1 == a;
 16         boolean e2 = a_1.equals(a);
 17         System.out.println(a_1);
 18     }
 19 
 20     //-128~127以内的Integer值
 21     static void integerPool() {
 22         Integer a1 = 127;
 23         Integer b1 = 127;
 24         //true
 25         boolean e = a1 == b1;
 26         //true
 27         boolean e2 = a1.equals(b1);
 28 
 29         System.out.println(e);
 30     }
 31 
 32 
 33     //-128~127以内的new Integer值
 34     static void integerPoolNewInteger() {
 35         Integer z1 = 127;
 36 
 37         //不使用常量池
 38         Integer a1 = new Integer(127);
 39         Integer b1 = new Integer(127);
 40 
 41         //引用地址同 a1
 42         Integer aa1 = a1;
 43         //引用地址同 b1
 44         Integer bb1 = b1;
 45         //引用地址同 z1
 46         Integer zz1 = z1;
 47 
 48         //使用常量池
 49         Integer c1 = Integer.valueOf("127");
 50         Integer d1 = Integer.parseInt("127");
 51 
 52         //false
 53         boolean e = a1 == b1;
 54         //true
 55         boolean e2 = a1.equals(b1);
 56 
 57         System.out.println(e);
 58     }
 59 
 60 
 61     //>=128
 62     static void integerPool128() {
 63         Integer a1 = 128;
 64         Integer b1 = 128;
 65 
 66         //false
 67         boolean e = a1 == b1;
 68         //true
 69         boolean e2 = a1.equals(b1);
 70 
 71         System.out.println(e);
 72     }
 73 
 74 
 75     static void decimalPool_1() {
 76         BigDecimal a1 = BigDecimal.ONE;
 77         BigDecimal a2 = BigDecimal.ONE;
 78 
 79         //true
 80         boolean e = a1 == a2;
 81         //true
 82         boolean e2 = a1.equals(a2);
 83 
 84         System.out.println(e);
 85 
 86     }
 87 
 88     static void decimalPool_2() {
 89         BigDecimal a1 = new BigDecimal(1);
 90         BigDecimal a2 = BigDecimal.ONE;
 91 
 92         //false
 93         boolean e = a1 == a2;
 94         //true
 95         boolean e2 = a1.equals(a2);
 96 
 97         System.out.println(e);
 98 
 99     }
100 
101     static void decimalPool_3() {
102         BigDecimal a1 = new BigDecimal(1);
103         BigDecimal a2 = new BigDecimal(1);
104 
105         //false
106         boolean e = a1 == a2;
107         //true
108         boolean e2 = a1.equals(a2);
109 
110         System.out.println(e);
111 
112     }
113 
114     //Byte,Short,Integer,Long,Character,Boolean。这5种包装类默认创建了数值[-128，127]的相应类型的缓存数据，但是超出此范围仍然会去创建新的对象
115     //浮点数类型的包装类Float,Double
116 }