java字符串类型String测试

public class StringDemo {
  public void test() {
    String a = "a";
    String b="a";
    String c=a;
    String aa = new String("a");
    String bb = new String("a");
    String cc = aa;
    String ab = "ab";
    String ab2 = "a"+"b";
    String ab3 = a + b;
    String ab4 = aa + bb;
    System.out.println();
    System.out.println(String.format("a==b：%s",a==b));
    System.out.println(String.format("a==c：%s",a==c));    
    System.out.println(String.format("a==aa：%s",a==aa));
    System.out.println(String.format("a==bb：%s",a==bb));
    System.out.println(String.format("a==cc：%s",a==cc));
    System.out.println(String.format("aa==bb：%s",aa==bb));
    System.out.println(String.format("aa==cc：%s",aa==cc));
    System.out.println(String.format("ab==ab2：%s",ab==ab2));
    System.out.println(String.format("ab==ab3：%s",ab==ab3));
    System.out.println(String.format("ab==ab4：%s",ab==ab4));
  }
}

结果：

a==b：true
a==c：true
a==aa：false
a==bb：false
a==cc：false
aa==bb：false
aa==cc：true
ab==ab2：true
ab==ab3：false
ab==ab4：false

内存标识：