这些表达式哪些是正确的？

[gxiaoqiang1987]

下列表达式哪些是正确的？
A、String s = “你好”; int i = 3; s+=i;
B、String s = “你好”; int i = 3; if(i==s){s+=I;}
C、String s = “你好”; int i = 3; s = i+s;
D、String s = “你好”; int i = 3; s=i+;
E、String s = null; int i = (s!=null)&&(s.length>0)?s.length():0;

请说名A到B行或不行的原因，不能只给出答案

[李敏910]

public class Test {
	public Test() {
		String s1 = "你好"; int i1 = 3; s1+=i1; 
		String s2 = "你好"; int i2 = 3; if(i2==s2){s2+=i2;} //s2是String类,不能直接等于
		String s3 = "你好"; int i3 = 3; s3 = i3+s3; 
		String s4 = "你好"; int i4 = 3; s4=i4++; //int不能直接赋值给string类型
		String s5 = null; int i5 = (s5!=null)&&(s5.length>0)?s5.length():0; 
		String s5 = null; int i5 = (s5!=null)&&(s5.length()>0)?s5.length():0; //length是方法,需要有()
	}

}