我有Java String，左右两边都有空格。我想从两边删除空白区域。
我试过的代码......
public class Test {
public static void main(String args[])
{
String abc = " Amebiasis ";
System.out.println(abc +" length "+abc.length());
System.out.println(rtrim(abc)+" length "+rtrim(abc).length());
System.out.println(ltrim(abc)+" length "+ltrim(abc).length());
String ltrim = abc.replaceAll("^\\s+","");
String rtrim = abc.replaceAll("\\s+$","");
System.out.println("ltrim"+ltrim);
System.out.println("rtrim"+rtrim);
}
public static String rtrim(String s) {
int i = s.length()-1;
while (i >= 0 && Character.isWhitespace(s.charAt(i))) {
i--;
}
return s.substring(0,i+1);
}
public static String ltrim(String s) {
int i = 0;
while (i < s.length() && Character.isWhitespace(s.charAt(i))) {
System.out.println("s.charAt(i) "+s.charAt(i));
i++;
}
return s.substring(i);
}
}
我得到的输出......
Amebiasis length 13
Amebiasis length 11
Amebiasis length 13
ltrim Amebiasis
rtrim Amebiasis
不知何故，它不会删除空格。我的代码有什么问题，请帮助我。
答案 0 :(得分：13)
默认可用trim()
String abc = " Amebiasis ";
System.out.println(""+abc.trim());
答案 1 :(得分：10)
我已经尝试了你的两个函数ltrim和rtrim，它们运行正常。如果我理解正确，您希望这些函数将更改字符串的内容。这是不可能的，因为Java中的字符串是immutable。如果您希望修剪字符串中的空格，然后继续使用剪裁后的字符串版本，则需要将rtrim或ltrim返回的值指定给abc变量：< / p>
String abc = " Amebiasis ";
abc = rtrim(abc); // abc now equals to " Amebiasis"
abc = ltrim(abc); // abc now equals to "Amebiasis"
答案 2 :(得分：6)
使用正则表达式从两边删除所有空格：
return str.replaceAll("\\s*$", "").replaceAll("^\\s*", "");
答案 3 :(得分：4)
使用Characters类，您可以轻松地左/右修剪任何给定字符（-class）的任何字符串：
// the demo function
var demo = function(){
/** fullScreenCanvas.js begin **/
// create a full document canvas on top
var canvas = (function(){
var canvas = document.getElementById("canv");
if(canvas !== null){
document.body.removeChild(canvas);
}
// creates a blank image with 2d context
canvas = document.createElement("canvas");
canvas.id = "canv";
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
canvas.style.position = "absolute";
canvas.style.top = "0px";
canvas.style.left = "0px";
canvas.style.zIndex = 1000;
canvas.ctx = canvas.getContext("2d");
document.body.appendChild(canvas);
return canvas;
})();
var ctx = canvas.ctx;
/** fullScreenCanvas.js end **/
/** MouseFull.js begin **/
// get the mouse data . This is a generic mouse handler I use so a little over kill for this example
var canvasMouseCallBack = undefined; // if needed
var mouse = (function(){
var mouse = {
x : 0, y : 0, w : 0, alt : false, shift : false, ctrl : false,
interfaceId : 0, buttonLastRaw : 0, buttonRaw : 0,
over : false, // mouse is over the element
bm : [1, 2, 4, 6, 5, 3], // masks for setting and clearing button raw bits;
getInterfaceId : function () { return this.interfaceId++; }, // For UI functions
startMouse:undefined,
};
function mouseMove(e) {
var t = e.type, m = mouse;
m.x = e.offsetX; m.y = e.offsetY;
if (m.x === undefined) { m.x = e.clientX; m.y = e.clientY; }
m.alt = e.altKey;m.shift = e.shiftKey;m.ctrl = e.ctrlKey;
if (t === "mousedown") { m.buttonRaw |= m.bm[e.which-1];
} else if (t === "mouseup") { m.buttonRaw &= m.bm[e.which + 2];
} else if (t === "mouseout") { m.buttonRaw = 0; m.over = false;
} else if (t === "mouseover") { m.over = true;
} else if (t === "mousewheel") { m.w = e.wheelDelta;
} else if (t === "DOMMouseScroll") { m.w = -e.detail;}
if (canvasMouseCallBack) { canvasMouseCallBack(m.x, m.y); }
e.preventDefault();
}
function startMouse(element){
if(element === undefined){
element = document;
}
"mousemove,mousedown,mouseup,mouseout,mouseover,mousewheel,DOMMouseScroll".split(",").forEach(
function(n){element.addEventListener(n, mouseMove);});
element.addEventListener("contextmenu", function (e) {e.preventDefault();}, false);
}
mouse.mouseStart = startMouse;
return mouse;
})();
if(typeof canvas === "undefined"){
mouse.mouseStart();
}else{
mouse.mouseStart(canvas);
}
/** MouseFull.js end **/
// some stuff to draw a grid
var gridStart= -(canvas.width/10)*4;
var gridEnd = (canvas.width/10)*14;
var gridStepMajor = canvas.width/10;
var gridStepMinor = canvas.width/20;
var minorCol = "#999";
var majorCol = "#000";
var minorWidth = 1;
var majorWidth = 3;
// some stuf to animate the transformation
var timer = 0;
var timerStep = 0.01;
//----------------------------------------------------------------------------
// the code from the answer
var matrix = [1, 0, 0, 1, 0, 0]; // normal matrix
var invMatrix = [1, 0, 0, 1]; // inverse matrix
function createMatrix(x, y, scale, rotate){
var m = matrix; // just to make it easier to type and read
var im = invMatrix; // just to make it easier to type and read
// create the scale and rotation part of the matrix
m[3] = m[0] = Math.cos(rotate) * scale;
m[2] = -(m[1] = Math.sin(rotate) * scale);
// translation
m[4] = x;
m[5] = y;
// calculate the inverse transformation
// first get the cross product of x axis and y axis
cross = m[0] * m[3] - m[1] * m[2];
// now get the inverted axies
im[0] = m[3] / cross;
im[1] = -m[1] / cross;
im[2] = -m[2] / cross;
im[3] = m[0] / cross;
}
// function to transform to world space
function toWorld(x,y){
var xx, yy, m;
m = invMatrix;
xx = x - matrix[4];
yy = y - matrix[5];
return {
x: xx * m[0] + yy * m[2] ,
y: xx * m[1] + yy * m[3]
}
}
//----------------------------------------------------------------------------
// center of canvas
var cw = canvas.width / 2;
var ch = canvas.height / 2;
// the main loop
function update(){
var i,x,y,s;
ctx.setTransform(1, 0, 0, 1, 0, 0); // reset the transform so we can clear
ctx.clearRect(0, 0, canvas.width, canvas.height); // clear the canvas
// animate the transformation
timer += timerStep;
x = Math.cos(timer) * gridStepMajor * 5 + cw; // position
y = Math.sin(timer) * gridStepMajor * 5 + ch;
s = Math.sin(timer/1.2) + 1.5; // scale
//----------------------------------------------------------------------
// create the matrix at x,y scale = s and rotation time/3
createMatrix(x,y,s,timer/3);
// use the created matrix to set the transformation
var m = matrix;
ctx.setTransform(m[0], m[1], m[2], m[3], m[4], m[5]);
//----------------------------------------------------------------------------
//draw a grid
ctx.lineWidth = 2;
ctx.beginPath();
ctx.strokeStyle = majorCol ;
ctx.lineWidth = majorWidth;
for(i = gridStart; i <= gridEnd; i+= gridStepMajor){
ctx.moveTo(gridStart, i);
ctx.lineTo(gridEnd, i);
ctx.moveTo(i, gridStart);
ctx.lineTo(i, gridEnd);
}
ctx.stroke();
ctx.strokeStyle = minorCol ;
ctx.lineWidth = minorWidth;
for(i = gridStart+gridStepMinor; i < gridEnd; i+= gridStepMinor){
ctx.moveTo(gridStart, i);
ctx.lineTo(gridEnd, i);
ctx.moveTo(i, gridStart);
ctx.lineTo(i, gridEnd);
}
ctx.stroke();
//---------------------------------------------------------------------
// get the mouse world coordinates
var mouseWorldPos = toWorld(mouse.x, mouse.y);
//---------------------------------------------------------------------
// marke the location with a cross and a circle;
ctx.strokeStyle = "red";
ctx.lineWidth = 3;
ctx.beginPath();
ctx.moveTo(mouseWorldPos.x - gridStepMajor, mouseWorldPos.y)
ctx.lineTo(mouseWorldPos.x + gridStepMajor, mouseWorldPos.y)
ctx.moveTo(mouseWorldPos.x, mouseWorldPos.y - gridStepMajor)
ctx.lineTo(mouseWorldPos.x, mouseWorldPos.y + gridStepMajor)
ctx.stroke();
ctx.fillStyle = "red";
ctx.strokeStyle = "yellow";
ctx.lineWidth = 4;
ctx.beginPath();
ctx.arc(mouseWorldPos.x, mouseWorldPos.y, 6, 0, Math.PI*2);
ctx.fill();
ctx.stroke();
ctx.fillStyle = "Blue";
ctx.setTransform(1,0,0,1,0,0);
ctx.font = "18px Arial";
var str = "Mouse canvas X: "+ mouse.x + " Y: " + mouse.y;
ctx.fillText(str , 10 ,18);
var str = "Mouse world X: "+ mouseWorldPos.x.toFixed(2) + " Y: " + mouseWorldPos.y.toFixed(2);
ctx.fillText(str , 10 ,36);
// if not over request a new animtion frame
if(!endItAll){
requestAnimationFrame(update);
}else{
// if done remove the canvas
var can = document.getElementById("canv");
if(can !== null){
document.body.removeChild(can);
}
// flag that we are ready to start again
endItAll = false;
}
}
update(); // start the animation
}
// Flag to indicate that the current execution should shut down
var endItAll = false;
// resizes but waits for the current running animnation to shut down
function resizeIt(){
endItAll = true;
function waitForIt(){
if(!endItAll){
demo();
}else{
setTimeout(waitForIt, 100);
}
}
setTimeout(waitForIt, 100);
}
// starts the demo
demo();
// listen to resize events and resize canvas if needed
window.addEventListener("resize",resizeIt)如果您想修剪空格，可以使用预定义的字符类：
Characters.valueOf('x').trim( ... )
Characters.valueOf('x').leftTrim( ... )
Characters.valueOf('x').rightTrim( ... )
该课程还有其他类型的角色操作，例如Characters.WHITESPACE.trim( ... )
Characters.WHITESPACE.leftTrim( ... )
Characters.WHITESPACE.rightTrim( ... )
，condense或replace。
答案 4 :(得分：1)
您的代码正常运行，问题中的输出错误，代码的实际输出为：
Amebiasis length 13
Amebiasis length 11
s.charAt(i)
s.charAt(i)
s.charAt(i)
s.charAt(i)
Amebiasis length 11
ltrimAmebiasis
rtrim Amebiasis
如果您只想修剪两侧，请执行
String abc = abc.trim();
答案 5 :(得分：0)
您只需要将修剪后的字符串对象分配给新字符串，因为字符串是不可变的，并且trim（）在具有相同地址时不能编辑该字符串。所以;
String abc = " Amebiasis ";
String abcTrimmed = abc.trim();
应该有用。
答案 6 :(得分：-1)
您可以使用\\S*
示例：
String name = "Hello :: World";
abc.replaceAll("\\s*::\\s*", "");
输出
HelloWorld