Question

我有以下简单的Java代码，试图理解使用'+'运算符的java中的字符串连接方式。

function calculateChange(){
  var amountDue = document.getElementById('amount-due').value;
  var amountReceived = document.getElementById('amount-received').value; 
  ////////////////////////////////////
  //dollars to print dollar mount  
  dollars = Math.floor(amountReceived % amountDue);
  document.getElementById("dollars-output").innerHTML = dollars;
                
  var quarters = Math.floor(amountReceived% dollars);
  document.getElementById('quarters-output').innerHTML = quarters;
  // var quarters to print # of quarters in change
                
  var dimes = Math.floor(amountReceived% dollars);
  document.getElementById('quarters-output').innerHTML = dimes;
  // var dimes to print # of dimes in change
                
  ///////////////////////////////////////
  var nickels = Math.floor(amountReceived% dollars);
  document.getElementById('quarters-output').innerHTML = nickels;  
  //var nickels to print # of nickels in change////////////////////////////////////
  //math.floor to do math
  //var pennies to print # of pennies in change        
  var pennies = Math.floor(amountReceived% dollars);
  document.getElementById('quarters-output').innerHTML = pennies; 
  return; 
  // to return the output of code
}

public class Problem { public static void main(String... args){ String str1 = "abc"; String str2 = "ab"; String str3 = "c"; String str4 = "ab" + "c";//This will use of StringBuilder class for concatenation and return new String object String str5 = str2 + str3;//This will use of StringBuilder class for concatenation and return new String object System.out.println(str1 == str4); // This returns true System.out.println(str1 == str5); // This returns false } }是2个字符串文字（str4和ab）的结果，而c是2个字符串文字（str5和{ {1}}）。在这两种情况下，java都将调用StringBuilder类来执行串联。

我相信这会导致在Java堆空间中创建2个不同的StringBuilder对象。

如果我的理解是正确的，为什么str2返回true？有人可以帮我弄清楚吗？

关于，曼尼什·沙玛

Answer 1

这取决于编译器和jvm如何对此进行优化。仅当两个变量都经过优化以指向相同的地址时，评估才是正确的。通常，使用==比较字符串是不可靠的。请改用“等于”方法。

字符串串联歧义

1 个答案: