new vs valueOf()

Code

Integer a = new Integer("1");
Integer b = new Integer("2");
System.out.println(a == b);	// false

Integer c = 1;
Integer d = 1;
System.out.println(c == d);	// true - because autoboxing uses valueOf() which use cached immutable values between -128..127

Integer e = 1000;
Integer f = 1000;
System.out.println(e == f);	// false because outside the cached values range

Result

Console

false
true
false

Bytecode

Compiled from "RunnContainer.java"
public class io.jpad.scratch.RunnContainer {
  public io.jpad.scratch.RunnContainer();
    Code:
       0: aload_0
       1: invokespecial #1                  // Method java/lang/Object."<init>":()V
       4: return

  public static void main(java.lang.String...) throws java.lang.Exception;
    Code:
       0: new           #2                  // class java/lang/Integer
       3: dup
       4: ldc           #3                  // String 1
       6: invokespecial #4                  // Method java/lang/Integer."<init>":(Ljava/lang/String;)V
       9: astore_1
      10: new           #2                  // class java/lang/Integer
      13: dup
      14: ldc           #5                  // String 2
      16: invokespecial #4                  // Method java/lang/Integer."<init>":(Ljava/lang/String;)V
      19: astore_2
      20: getstatic     #6                  // Field java/lang/System.out:Ljava/io/PrintStream;
      23: aload_1
      24: aload_2
      25: if_acmpne     32
      28: iconst_1
      29: goto          33
      32: iconst_0
      33: invokevirtual #7                  // Method java/io/PrintStream.println:(Z)V
      36: iconst_1
      37: invokestatic  #8                  // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
      40: astore_3
      41: iconst_1
      42: invokestatic  #8                  // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
      45: astore        4
      47: getstatic     #6                  // Field java/lang/System.out:Ljava/io/PrintStream;
      50: aload_3
      51: aload         4
      53: if_acmpne     60
      56: iconst_1
      57: goto          61
      60: iconst_0
      61: invokevirtual #7                  // Method java/io/PrintStream.println:(Z)V
      64: sipush        1000
      67: invokestatic  #8                  // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
      70: astore        5
      72: sipush        1000
      75: invokestatic  #8                  // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
      78: astore        6
      80: getstatic     #6                  // Field java/lang/System.out:Ljava/io/PrintStream;
      83: aload         5
      85: aload         6
      87: if_acmpne     94
      90: iconst_1
      91: goto          95
      94: iconst_0
      95: invokevirtual #7                  // Method java/io/PrintStream.println:(Z)V
      98: return
}

Jpad Version:1.07

viewCount:1842

Creator: graemeg

Latest Editor: graemeg

new vs valueOf()

Code

Result

Console

Bytecode

Tags