java中如何区分==和equals

  Integer a=1000;
  Integer b=1000;
  System.out.println(a == b);//false
  System.out.println(a.equals(b));//true 

   Integer a1=127;
   Integer a2=127;
   System.out.println(a1 == a2);//true
   System.out.println(a1.equals(a2));//true

private static class IntegerCache {
  static final int low = -128;
  static final int high;
  static final Integer cache[];

  static {
   // high value may be configured by property
   int h = 127;
   String integerCacheHighPropValue =
    sun.misc.VM.getSavedProperty("java.lang.Integer.IntegerCache.high");
   if (integerCacheHighPropValue != null) {
    try {
     int i = parseInt(integerCacheHighPropValue);
     i = Math.max(i, 127);
     // Maximum array size is Integer.MAX_VALUE
     h = Math.min(i, Integer.MAX_VALUE - (-low) -1);
    } catch( NumberFormatException nfe) {
     // If the property cannot be parsed into an int, ignore it.
    }
   }
   high = h;

   cache = new Integer[(high - low) + 1];
   int j = low;
   for(int k = 0; k < cache.length; k++)
    cache[k] = new Integer(j++);

   // range [-128, 127] must be interned (JLS7 5.1.7)
   assert IntegerCache.high >= 127;
  }

  private IntegerCache() {}
 }

package a;

public class Student {
 static class A{
  @Override
  public boolean equals(Object obj) {
   return true;
  }
 }
 static class B{

 }

 public static void main(String[] args) {
  A a=new A();
  System.out.println(a.equals(new B()));
 }
}