java基础：int和Integer的区别？

int和Integer的区别

区别	int	Integer
类型	基本数据类型	引用类型
默认值	null

现象

int 和 Integer == 比较

public void test1() {
        Integer i1 = 100;
        int j1 = 100;

        Integer i2 = 200;
        int j2 = 200;

        System.out.println(i1 == j1); // true
        System.out.println(i2 == j2); // true
    }

追本溯源：javap -c TestInteger.class

public void test1();
    Code:
       0: bipush        100
       2: invokestatic  #2                  // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
       5: astore_1
       6: bipush        100
       8: istore_2
       9: sipush        200
      12: invokestatic  #2                  // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
      15: astore_3
      16: sipush        200
      19: istore        4
      21: getstatic     #3                  // Field java/lang/System.out:Ljava/io/PrintStream;
      24: aload_1
      25: invokevirtual #4                  // Method java/lang/Integer.intValue:()I
      28: iload_2
      29: if_icmpne     36
      32: iconst_1
      33: goto          37
      36: iconst_0
      37: invokevirtual #5                  // Method java/io/PrintStream.println:(Z)V
      40: getstatic     #3                  // Field java/lang/System.out:Ljava/io/PrintStream;
      43: aload_3
      44: invokevirtual #4                  // Method java/lang/Integer.intValue:()I
      47: iload         4
      49: if_icmpne     56
      52: iconst_1
      53: goto          57
      56: iconst_0
      57: invokevirtual #5                  // Method java/io/PrintStream.println:(Z)V
      60: return

Integer 和 Integer == 比较

public void test2() {
        Integer i1 = 100;
        Integer j1 = 100;

        Integer i2 = 200;
        Integer j2 = 200;

        System.out.println(i1 == j1); // true
        System.out.println(i2 == j2); // false
    }

public void test2();
    Code:
       0: bipush        100
       2: invokestatic  #2                  // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
       5: astore_1
       6: bipush        100
       8: invokestatic  #2                  // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
      11: astore_2
      12: sipush        200
      15: invokestatic  #2                  // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
      18: astore_3
      19: sipush        200
      22: invokestatic  #2                  // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
      25: astore        4
      27: getstatic     #3                  // Field java/lang/System.out:Ljava/io/PrintStream;
      30: aload_1
      31: aload_2
      32: if_acmpne     39
      35: iconst_1
      36: goto          40
      39: iconst_0
      40: invokevirtual #5                  // Method java/io/PrintStream.println:(Z)V
      43: getstatic     #3                  // Field java/lang/System.out:Ljava/io/PrintStream;
      46: aload_3
      47: aload         4
      49: if_acmpne     56
      52: iconst_1
      53: goto          57
      56: iconst_0
      57: invokevirtual #5                  // Method java/io/PrintStream.println:(Z)V
      60: return

int 和 new Integer == 比较

public void test3() {
        Integer i1 = new Integer(100);
        int j1 = 100;

        Integer i2 = new Integer(200);
        int j2 = 200;

        System.out.println(i1 == j1); // true
        System.out.println(i2 == j2); // true
    }

public void test3();
    Code:
       0: new           #6                  // class java/lang/Integer
       3: dup
       4: bipush        100
       6: invokespecial #7                  // Method java/lang/Integer."<init>":(I)V
       9: astore_1
      10: bipush        100
      12: istore_2
      13: new           #6                  // class java/lang/Integer
      16: dup
      17: sipush        200
      20: invokespecial #7                  // Method java/lang/Integer."<init>":(I)V
      23: astore_3
      24: sipush        200
      27: istore        4
      29: getstatic     #3                  // Field java/lang/System.out:Ljava/io/PrintStream;
      32: aload_1
      33: invokevirtual #4                  // Method java/lang/Integer.intValue:()I
      36: iload_2
      37: if_icmpne     44
      40: iconst_1
      41: goto          45
      44: iconst_0
      45: invokevirtual #5                  // Method java/io/PrintStream.println:(Z)V
      48: getstatic     #3                  // Field java/lang/System.out:Ljava/io/PrintStream;
      51: aload_3
      52: invokevirtual #4                  // Method java/lang/Integer.intValue:()I
      55: iload         4
      57: if_icmpne     64
      60: iconst_1
      61: goto          65
      64: iconst_0
      65: invokevirtual #5                  // Method java/io/PrintStream.println:(Z)V
      68: return

Integer 和 new Integer == 比较

public void test4() {
        Integer i1 = new Integer(100);
        Integer j1 = 100;

        Integer i2 = new Integer(200);
        Integer j2 = 200;

        System.out.println(i1 == j1); // false
        System.out.println(i2 == j2); // false
    }

public void test4();
    Code:
       0: new           #6                  // class java/lang/Integer
       3: dup
       4: bipush        100
       6: invokespecial #7                  // Method java/lang/Integer."<init>":(I)V
       9: astore_1
      10: bipush        100
      12: invokestatic  #2                  // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
      15: astore_2
      16: new           #6                  // class java/lang/Integer
      19: dup
      20: sipush        200
      23: invokespecial #7                  // Method java/lang/Integer."<init>":(I)V
      26: astore_3
      27: sipush        200
      30: invokestatic  #2                  // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
      33: astore        4
      35: getstatic     #3                  // Field java/lang/System.out:Ljava/io/PrintStream;
      38: aload_1
      39: aload_2
      40: if_acmpne     47
      43: iconst_1
      44: goto          48
      47: iconst_0
      48: invokevirtual #5                  // Method java/io/PrintStream.println:(Z)V
      51: getstatic     #3                  // Field java/lang/System.out:Ljava/io/PrintStream;
      54: aload_3
      55: aload         4
      57: if_acmpne     64
      60: iconst_1
      61: goto          65
      64: iconst_0
      65: invokevirtual #5                  // Method java/io/PrintStream.println:(Z)V
      68: return

Integer 和 new Integer equals 比较

public void test5() {
        Integer i1 = new Integer(100);
        Integer j1 = 100;

        Integer i2 = new Integer(200);
        Integer j2 = 200;

        System.out.println(i1.equals(j1)); // true
        System.out.println(i2.equals(j2)); // true
    }

public void test5();
    Code:
       0: new           #6                  // class java/lang/Integer
       3: dup
       4: bipush        100
       6: invokespecial #7                  // Method java/lang/Integer."<init>":(I)V
       9: astore_1
      10: bipush        100
      12: invokestatic  #2                  // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
      15: astore_2
      16: new           #6                  // class java/lang/Integer
      19: dup
      20: sipush        200
      23: invokespecial #7                  // Method java/lang/Integer."<init>":(I)V
      26: astore_3
      27: sipush        200
      30: invokestatic  #2                  // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
      33: astore        4
      35: getstatic     #3                  // Field java/lang/System.out:Ljava/io/PrintStream;
      38: aload_1
      39: aload_2
      40: invokevirtual #8                  // Method java/lang/Integer.equals:(Ljava/lang/Object;)Z
      43: invokevirtual #5                  // Method java/io/PrintStream.println:(Z)V
      46: getstatic     #3                  // Field java/lang/System.out:Ljava/io/PrintStream;
      49: aload_3
      50: aload         4
      52: invokevirtual #8                  // Method java/lang/Integer.equals:(Ljava/lang/Object;)Z
      55: invokevirtual #5                  // Method java/io/PrintStream.println:(Z)V
      58: return

知识点

自动装箱拆箱

自动装箱

Integer i = 100; // Integer.valueOf(100)

自动拆箱

integer.intValue()

Integer源码核心方法

Integer.valueOf

/**
     * Returns an {@code Integer} instance representing the specified
     * {@code int} value.  If a new {@code Integer} instance is not
     * required, this method should generally be used in preference to
     * the constructor {@link #Integer(int)}, as this method is likely
     * to yield significantly better space and time performance by
     * caching frequently requested values.
     *
     * This method will always cache values in the range -128 to 127,
     * inclusive, and may cache other values outside of this range.
     *
     * @param  i an {@code int} value.
     * @return an {@code Integer} instance representing {@code i}.
     * @since  1.5
     */
    public static Integer valueOf(int i) {
        if (i >= IntegerCache.low && i <= IntegerCache.high)
            return IntegerCache.cache[i + (-IntegerCache.low)];
        return new Integer(i);
    }

equals

/**
     * Compares this object to the specified object.  The result is
     * {@code true} if and only if the argument is not
     * {@code null} and is an {@code Integer} object that
     * contains the same {@code int} value as this object.
     *
     * @param   obj   the object to compare with.
     * @return  {@code true} if the objects are the same;
     *          {@code false} otherwise.
     */
    public boolean equals(Object obj) {
        if (obj instanceof Integer) {
            return value == ((Integer)obj).intValue();
        }
        return false;
    }

扩展

java中基本类型的包装类的大部分都实现了常量池技术，Byte,Short,Integer,Long,Character,Boolean

常量池技术使用设计模式：享元模式实现。

最佳实践

当 int 与 Integer 进行 == 比较时，JVM会将 Integer 进行自动拆箱。
基本类型参与比较时，可以使用 ==
两个对象类型比较时，可以使用 equals() 比较数值
两个对象类型比较时，可以使用 == 比较是否为同一个对象

java基础：int和Integer的区别？

int和Integer的区别

现象

int 和 Integer == 比较

追本溯源：javap -c TestInteger.class

Integer 和 Integer == 比较

int 和 new Integer == 比较

Integer 和 new Integer == 比较

Integer 和 new Integer equals 比较

知识点

自动装箱拆箱

自动装箱

自动拆箱

Integer源码核心方法

Integer.valueOf

equals

扩展

最佳实践

Github代码案例

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